Driving mechanism for an index wheel



Aug. 4, 1959 D. FRlTscH 2,897,680

DRIVING MECHANISM FOR AN INDEX wam-:L

Filed Deo. 31, 1956 D574) /EL /TJ c /7/ BYvMw/Qt ATTORNEY United States Patent rifice DRIVING MEcHANIsM Eon AN INDEX WHEEL Daniel Fritsch, Lancaster, Pa., assigner to Hamilton Watch Company, Lancaster, Pa., a corporation of Penn- Sylvania Application December 31, 1956, Serial No. 631,689

2 Claims. (Cl. 74-126) This invention relates to watch construction and more particularly relates to a driving mechanism for an index wheel.

In a conventional spring driven watch a main spring transmits power through a train to an escapement which, in combination with a balance assembly, regulates the rate at which the main spring is allowed to move the time indicating elements or hands of the watch. In such watches the rate of rotation of the escape wheel is controlled by a pallet and fork cooperating with a roller on a roller table carried by the staff of the balance wheel. The escape wheel is constantly in a state of tension, that is, in a state in which it is attempting to deliver power.

In electric watches of the type described in assignees co-pending applications, Serial Nos. 409,934 and 578,843 led February l2, 1954, and April 17, 1956, respectively, the balance wheel no longer regulates the escape of power from a separate power source, such as the main spring of a conventional watch, but itself provides the driving motion which is imparted to the train and watch hands. The train is no longer under a constant tension so that a different means of transferring the oscillating motion of the balance wheel into the rotary motion of the train may be provided.

It is accordingly a primary object of the present invention to provide a driving mechanism for an index wheel for transforming rotary oscillatory motion into step by step rotary motion.

It is another object of the invention to provide a simple and effective mechanism for imparting a step by step motion to the index wheel of a watch from the oscillatory motion of the balance staff through the use of a resilient drive connection which minimizes shock to the oscillating balance wheel and which eliminates jamming of the index mechanism.

It is still another object of the invention to provide a means for driving the index wheel of a watch from a balance staff through a resilient spring which prevents an impact shock to the balance wheel at the moment power delivery commences.

It is a still further object of the invention to provide a means for translating the oscillatory motion of a balance wheel into step by step rotary motion in an index wheel comprising a generally spiral screw carried by the balance wheel assembly.

These and further objects and advantages of the invention will become apparent upon reference to the following specification and claims and appended drawings wherein:

Figure l is a vertical elevation, partly in section, showing a driving mechanism constructed according to the present invention; and

Figure 2 is a horizontal section taken along the line 2-2 of Figure l.

Referring to Figure 1, there is shown the balance assembly of a watch consisting of a balance wheel carried by a balance staff 12 having its lower end journaled in a conventional bearing assembly containing a hole Patented Aug. 4, 1959 jewel 14 and cap jewel 16 mounted in pillar plate 18. A hair spring 20 is carried on hair spring collet 22 on the staff 12 in the conventional manner.

Mounted upon the steif 12 beneath balance wheel 10 is a collet 24 which carries one end of a generally spiral drive spring 26 which terminates in a rounded end 28.

Mounted adjacent the spring 26 in suitable bearings, not shown, is a toothed index wheel 30 which is carried on a shaft 32. The index wheel 30 is provided with teeth 34 having one surface 36 which is substantially radial and having a second and longer surface 38. The surface 38 is at an angle with respect to the surface 36 which will permit the spring end 28 to engage the surface 36 on a tooth 40 substantially at right angles thereto and without striking the surface 38 on an adjacent tooth 42, as seen in Figure 2.

A detent jewel pin 44, ywhich is generally semi-circular in shape or of the same general shape as a roller jewel, is resiliently urged into adjacent teeth on the index wheel 30 by means of a tension spring 46. The spring 46 may be secured to the watch structure in any suitable manner, as by means of a block 48 fastened to the pillar plate 18 by means of a screw 50. Tension spring 46 may be secured to block 48 by means of mounting screws 52.

In operation, the end 28 of spiral spring 26 moves in a counterclockwise direction as the balance wheel oscillates and engages at substantially a right angle the radial surface 36 of a tooth 40. The spring 26 which is unrestrained from its point of contact to its attachment to the collet 24 is then unwound a certain amount before the pressure of its end 2S on tooth `40 causes the index wheel 30 to start to move against the indexing or locking force applied by the jewel 44 and tension spring 46. Because of this resiliency the balance wheel does not receive an abrupt shock at the start of power delivery and may continue its oscillation with less abrupt interference than if it delivered power to the index 'wheel through a direct and non-resilient connection.

Under the drive of spring 26, the index wheel 30 moves a distance of one tooth. This increment of movement is determined by the indexing jewel 44 and also by the fact that the end 28 of spiral spring 26 escapes from the radial surface 36 after a movement of one tooth has been accomplished.

The tension spring 46 snaps the index jewel 44 into the space between the next two teeth to lock the index wheel 30 in this advanced position while the spiral spring continues to rotate in a counterclockwise direction. Hair spring 22 thereupon reverses the direction of the balance wheel 10, carrying the spiral spring 26 in a clockwise direction. As the spring moves in this direction, its end 28 brushes by the long surface 38 of a tooth on the index wheel 30. No motion is imparted to the index wheel, however, inasmuch as no drive connection is established and the end 28 of spiral spring 26 is merely deflected toward the balance staff by reason of the resiliency of the helicoidal spring. Movement is also prevented by the jewel 44 which prevents backward motion.

According to the invention there is thus provided a novel means of delivering pofwer from an oscillating balance wheel to an index wheel through a resilient connection which avoids transmitting abrupt shock to the balance wheel. Because of the resiliency of the drive spring it cannot jam in engagement with the index wheel and thus eliminates a cause of watch stoppage.

The invention may be embodied in other specific forms without departing from the spirit of essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein,

What is claimed and desired to be secured by the United States Letters Patent is:

1. An index wheel driving mechanism for watches comprising a toothed index wheelV mounted for rotation, an oscillating shaft, a collet frictionally mounted on said oscillating shaft, a spiral spring freely mounted for expansion and contraction supported by said collet at a rst end only, said spiral spring lying substantially in a plane and having a second end engageable with the teeth of said index wheel `to drive it a fraction of a turn, said spiral spring further being unrestrained from the point of Contact of said second end with said teeth through an angle in excess of 180.

2. An index Wheel driving mechanism for Watches as set out in claim 1 wherein said second end of said spiral spring initially contacts the teeth of said index Wheel with the terminal portion of said spiral spring being substantially at right angles to the face of the teeth of said index wheel.

References Cited in the le of this patent UNITED STATES PATENTS 2,084,226 Strahm June 15, 1937 2,486,043 Lofgren Oct. 25, 1949 2,487,733 Scheffer Nov. 8, 1949 2,511,349 Klay June 13, 1950 2,757,555 Ensign et al. Aug. 7, 1956 2,789,411 Ensign et al Apr. 23, 1957 FOREIGN PATENTS 609,642 Great Britain Oct. 5, 1948 

